DESCRIPTION: Two lines of study, one dealing with factors that initiate higher plant cell division and the other involving pathogenesis in a prokaryotic pathogen of this plant, have intersected at a single xenognostic growth factor involved in the control of both events. Structural analysis of the growth factor has led to a mechanistic model for the activation event. This model has provided valuable insight and enabled the development of both reversible and irreversible specific inhibitors of Agrobacterium tumefaciens virulence gene expression. By exploiting the inhibitors and the molecular genetics of the pathogen, specific receptor proteins, Xpb proteins, have been identified. The outlined experiments will (i) isolate and characterize the Xpa proteins, (ii) characterize the mechanism by which the growth factor-Xpb complex activates a two-component phosphorylation cascade controlling virulence gene expression, (iii) select and characterize mutants that alter sensitivity to the growth factor, and (iv) analyze specific mutants of the autokinase involved in the signal transduction. Successful completion of the proposed experiments will significantly expand our understanding of phenolic perception of prokaryotes, providing at least a model, if not the proteins for eukaryotic perception, as well as provide the first insight into how two-component regulatory systems recognize and transduce signal output. Related growth factors serve critical roles in animal and plant systems and the opportunity to study the mechanism of these factors in the context of pathogenesis is unique. The knowledge gained will provide insight into the control of eukaryotic cell division as well as define strategies involved in pathogenesis. Two laboratories have combined their expertise in order to exploit the chemical, biochemical and molecular genetic approaches necessary for the efficient execution of these experiments.